1. Field of Invention
This invention relates generally to computer graphics, and in particular to a key matrix making it possible for an operator who views a computer terminal graphics display to manipulate a cursor to occupy selected action points thereon.
2. Status of Prior Art
Involved in computer graphics is communication between an operator and a computer wherein the input and output of the computer takes the form of charts, drawings or pictorial representations. Thus computer graphics may be a line drawing of a two or three dimensional abstraction, the structural component of a building or a flow chart.
In an industrial process control system, the several process variables to be controlled, such as flow rate, pressure and temperature are sensed by individual transducers each included in a local process loop. In direct digital control, the several local control loops of a given installation are governed by a computer having a CRT display terminal on which one may graphically display the process being controlled and alphanumeric data relating thereto.
Thus in a chemical processing plant in which say a process is carried out in a reactor into which is fed through respective control valves various chemicals and catalysts as well as steam under pressure derived from a steam generator, among the process variables are the flowrates of the inflowing chemicals into the reactor, the timing of the reaction, the level of temperature within the reactor, the flowrate of the product discharged from the reactor as well as the steam pressure. In a computer-controlled system, a schematic or flow chart of the reactor process is graphically presented on the cathode ray tube terminal before which is an operator console making it possible for the operator to single out any process varaable on the display and to exercise control thereover.
In order for an operator to select any process variable in a computer graphics display, the use of a cursor for this purpose is often employed. A cursor is a symbol or special character serving as a pointer to allow interaction between the console operator and the display. It may take the form of a blinking luminous dot, an inverted V or caret, or any other distinctive symbol.
Alphanumeric keyboards usually include special keys or a cursor matrix adapted to shift the position of a cursor to the left or right, or up or down, as well as a "home" key. Thus, the usual key matrix is constituted by a home key surrounded by four "arrow" keys to effect movement of the cursor away from the home position along the X or Y axis.
If, therefore, the cursor is initially at its "home" position near the upper left-hand corner of a graphics display and the operator wishes by way of the cursor matrix to select a control point on the display near its center, he cannot with the conventional cursor matrix cause the cursor to slew or move along a diagonal in the shortest path toward the control point. He can only advance the cursor first to the right in the X direction to a point above the control point and in vertical alignment therewith, and then move the cursor in the Y direction down to the control point, the operator being careful not to overshoot.
It is for this reason that on a graphics control console, the cursor symbol is usually manipulated by a manual input device such as a joystick, a data tablet, a trackball, a forcestick or a mouse. In the case of a joystick, for example, the operator can, as it were, drive the cursor around the screen to a point where it coincides with the exact X-Y location of the desired control point on the graphics display. However, the use of joysticks and other expedients in conjunction with operator keyboards adds substantially to the cost of the computer graphics and has other disadvantages, such as low speed of operation, overshoot and excessive computer processing load.